Water Vapor Behavior in Exterior Insulation and Finish Systems

Exterior Insulation and Finish Systems (EIFS's) are a type of cladding for exterior building walls. They are attached to the outside face of the wall structure. EIFS's were developed in Europe where exterior wall structures are predominantly unit masonry and concrete. In America, EIFS's are usually attached to lightweight wall structures of studs and gypsum sheathing.

In America, EIFS's are used in a wide range of climate conditions, including air conditioned buildings in hot, humid climates as well as arctic conditions. EIFS's are used in virtually every type of building including residential and high-rise commercial structures. Because of their light weight and relatively short track record, the longevity of EIFS's has been questioned. In particular, the effects of water from both liquid and water vapor sources is a concern. This concern has come from both field experience and theoretical analysis.

The American way of using EIFS's results in different water vapor behavior in the wall assembly. Condensation can occur in different locations in the wall under different conditions. The effects of water on the wall can be pronounced. The durability of the wall can be greatly affected if water vapor problems occur.

This paper reviews the American style of using EIFS's on light weight wall structures in terms of water vapor flow behavior. A computer program is used to demonstrate various conditions that affect the development of condensation in EIFS wall systems. The paper identifies common American wall designs that require attention and offers solutions for dealing with water vapor problems.